Quick Answer: The best tankless water heater for most homes with a gas line is the Rinnai RU199iN — a condensing 199,000 BTU unit rated up to 11 GPM at a 0.96 UEF with WiFi control. The Navien NPE-240A2 is the pick if you want built-in recirculation for instant hot water, while the Rheem Performance Platinum 9.5 GPM is the best value at retail. No gas line? The Stiebel Eltron Tempra 36 Plus is the best whole-home electric unit, and the EcoSmart ECO 27 is the budget electric choice. Remember: every GPM rating below assumes a warm inlet — real flow drops in cold climates.
A tankless (or “on-demand”) water heater fires only when you open a hot tap, so it never runs out and doesn’t waste energy keeping a tank warm 24/7. We compared gas, propane, and electric units across flow rate (GPM), efficiency (UEF), venting, and real install cost to find the ones worth buying in 2026. Because tankless GPM depends on how cold your incoming water is, we’ve framed every flow figure as a warm-climate maximum — your winter numbers will be lower.
Our top picks at a glance
| Model | Best for | Fuel | Max Flow / Power | Price |
|---|---|---|---|---|
| Rinnai RU199iN | Best overall | Natural gas | ~11 GPM · 199k BTU | ~$1,600 |
| Navien NPE-240A2 | Best with recirculation | Natural gas | ~11.2 GPM · 199k BTU | ~$1,500 |
| Rheem Performance Platinum 9.5 | Best value (retail) | Gas / propane | 9.5 GPM · 199k BTU | ~$1,150 |
| Stiebel Eltron Tempra 36 Plus | Best whole-home electric | Electric 240V | 36 kW · ~7 GPM | ~$850 |
| EcoSmart ECO 27 | Best budget electric | Electric 240V | 27 kW · ~6.6 GPM | ~$570 |
By the numbers
- 24–34% more efficient than a storage tank for homes using 41 gallons/day or less (8–14% for high-use homes). — U.S. Department of Energy
- ~$95/year saved by a family of four with an ENERGY STAR gas tankless vs. a standard gas tank — roughly $1,800 over the unit’s life. — ENERGY STAR
- ~20 years typical tankless lifespan vs. 10–12 years for a tank. — DOE / industry
- Up to $600 federal 25C tax credit for qualifying high-efficiency gas tankless units (verify current rules for your install year).
1. Rinnai RU199iN — Best Overall
Rinnai RU199iN Condensing Gas Tankless
- 199,000 BTU condensing burner delivers up to ~11 GPM in warm climates — enough for 2–3 fixtures at once.
- 0.96 UEF efficiency and PVC venting keep operating cost and install cost down versus non-condensing units.
- Built-in WiFi (Control-R) and a 12-year heat-exchanger warranty.
- Typically runs $100–$300 less than the comparable Navien.
The RU199iN is the unit we recommend to most homeowners with natural gas. It sits at the top of Rinnai’s condensing RU Series (above the mid-tier RL and entry RE lines), and its 199k BTU output means it rarely runs short even when the laundry and a shower are both going. Confirm the exact SKU before you buy — Rinnai has migrated part of this line to RX199iN branding in some channels, and you’ll want to match natural gas vs. propane and indoor vs. outdoor to your setup. For the full gas shortlist, see our best gas tankless water heater guide.
2. Navien NPE-240A2 — Best With Recirculation
Navien NPE-240A2 Condensing Gas Tankless
- ComfortFlow built-in recirculation pump and buffer tank cut the wait for hot water at the tap.
- Up to ~11.2 GPM and a 0.96–0.97 UEF put it among the most efficient whole-home units.
- Class-leading 15-year heat-exchanger warranty.
If the annoyance you most want to solve is standing at the shower waiting for hot water, the Navien NPE-240A2 is the answer. Its built-in recirculation pump and small buffer tank tame the “cold-water sandwich” that plagues some tankless units, and the 15-year warranty is the longest here. You pay a little more than the Rinnai for those features.
3. Rheem Performance Platinum 9.5 GPM — Best Value
Rheem Performance Platinum 9.5 GPM (ECOH200) Gas Tankless
- Condensing 199,000 BTU unit rated 9.5 GPM — plenty for most 2–3 bath homes.
- ENERGY STAR certified with EcoNet WiFi; convertible for indoor or outdoor install.
- Sold at major retailers, so it's the easiest premium unit to buy and service yourself.
Rheem’s retail Performance Platinum line (the smart “ECOH” SKUs — not to be confused with Rheem’s pro RTGH series) is the value sweet spot in gas tankless. You get condensing efficiency, WiFi, and 9.5 GPM for a few hundred dollars less than the Rinnai or Navien. It’s our pick for a budget-conscious whole-home gas upgrade.
4. Stiebel Eltron Tempra 36 Plus — Best Whole-Home Electric
Stiebel Eltron Tempra 36 Plus Electric Tankless
- 36 kW of power delivers up to ~7 GPM in warm and moderate climates.
- Advanced Flow Control automatically throttles flow slightly to hold your set temperature instead of running cold.
- ~99% thermal efficiency and no venting — but needs serious 240V service (roughly 150A across multiple breakers).
When there’s no gas line, the Tempra 36 Plus is the best whole-home electric unit we’d buy. Its Advanced Flow Control is the standout: instead of letting output go tepid when demand spikes, it gently reduces flow to keep your water at temperature. Just budget for the electrical work — 36 kW is a big load. See our full electric tankless roundup and the electric vs gas breakdown before committing.
5. EcoSmart ECO 27 — Best Budget Electric
EcoSmart ECO 27 Electric Tankless
- 27 kW self-modulating unit rated up to ~6.6 GPM in warm climates, with a low 0.3 GPM activation flow.
- Compact wall unit with digital temperature control and a lifetime limited warranty (conditions apply).
- Great value for a warm-climate 2-bath home or a sunbelt build.
The EcoSmart ECO 27 gives you real whole-home electric performance for well under $600. Note that its “lifetime” warranty asks for annual maintenance, professional installation, and a water softener on hard water to stay valid — reasonable conditions, but worth knowing. In cold-inlet regions, step up to the 36 kW ECO 36 or a Rheem RTEX-36.
How to choose a tankless water heater
- Fuel: Have a gas line and a big household? Go gas for the higher flow. No gas, warm climate, or a smaller home? Electric is cheaper to buy and install.
- Flow rate (GPM): Size to your peak simultaneous demand — roughly 5.5–7.5 GPM for most homes. Remember every rating is a warm-climate maximum; cold incoming water can cut it in half.
- Efficiency (UEF): Condensing gas units hit ~0.93–0.97 UEF; non-condensing run ~0.81–0.82 but cost less and need stainless venting. Electric is ~98–99% at the unit.
- Install reality: Gas may need a bigger gas line and venting; high-power electric may need a 150–200A panel and new circuits. Get a quote before you buy the unit.
- Recirculation: If you hate waiting for hot water, choose a unit with built-in or add-on recirculation (like the Navien).
The bottom line
For most homes with natural gas, the Rinnai RU199iN is the tankless water heater to buy: 11 GPM, condensing efficiency, WiFi, and a lower price than the comparable Navien. Want instant hot water? The Navien NPE-240A2 adds built-in recirculation. Shopping at retail on a budget? The Rheem Performance Platinum 9.5 GPM delivers. And with no gas line, the Stiebel Eltron Tempra 36 Plus (or the value EcoSmart ECO 27) is the electric pick. Still deciding whether tankless is worth it at all? Read our tankless vs tank guide.